A corresponding solution from the field of the process automation is already described in WO 2004/013585 A1. In automation technology, especially in process automation technology, field devices are applied, which are used for determining and monitoring process variables. Examples of such field devices are fill level measuring devices, flow measuring devices, analytical measuring devices, pressure and temperature measuring devices, moisture and conductivity measuring devices, density and viscosity measuring devices. The sensors of these field devices register the corresponding process variables, for example fill level, flow, pH-value, substance concentration, pressure, temperature, moisture, conductivity, density or viscosity.
Also subsumed under the term “field devices” are, however, actuators (e.g. valves or pumps), via which, for example, the flow a liquid in a pipeline or the fill level in a container can be changed. A large number of such field devices are available from members of the firm, Endress + Hauser.
In modern automation technology plants, as well as in the automobile sector, field devices are, as a rule, connected via communication networks (such as HART multidrop, point to point connection, Profibus, Foundation Fieldbus, or CAN-bus) with a superordinated unit, which is referred to as a control system or superordinated control unit. This superordinated unit serves to perform control, diagnostic and visualizing functions, and is also used for monitoring, starting up and servicing the field devices. Additional components necessary for operation of fieldbus systems and directly connected to a fieldbus (especially components used for communication with the superordinated units) are likewise frequently referred to as field devices. These supplemental components include, for example, remote I/Os, gateways, linking devices, controllers or wireless adapters.
The software portion of field devices is constantly increasing. The advantage of the use of microcontroller-controlled, intelligent field devices (smart field devices) lies in the fact that a large number of different functionalities can be implemented in a field device via application-specific software programs; program changes can also be performed relatively easily. On the other hand, the high flexibility of program-controlled field devices is countered by a relatively low processing speed—and therewith a correspondingly low measuring rate—as a result of the sequential progression through the program.
In order to increase processing speed, ASICs (Application Specific Integrated Circuits) are always used in these field devices, whenever such makes sense. Through application-specific configuration, these chips can process data and signals substantially faster than a software program can. ASICs are especially excellently suited for computationally intensive applications.
A disadvantage in the application of ASICs is the fact that the functionality of these chips is firmly predetermined. A subsequent change in functionality is not readily possible in the case of these chips. Furthermore, the use of ASICs is only worthwhile in the case of a relatively large number of pieces, since the developmental effort and the therewith connected costs are high.
In order to avoid the drawbacks of the firmly predetermined functionality, in WO 03/098154 A1, a configurable field device is described, in the case of which a reconfigurable logic chip is provided in the form of an FPGA. In this known solution, the logic chip—which has at least one microcontroller, which is also referred to as an embedded controller—is configured during system start. After the configuration is finished, the required software is loaded into the microcontroller. The reconfigurable logic chip required in such case must have at its disposal sufficient resources (particularly logic, wiring and memory resources) in order to fulfill the desired functionalities. Logic chips with many resources require a great deal of energy, which, again, from a functional point of view, makes use thereof in automation possible only to a limited degree. A disadvantage of using logic chips with few resources (and, thus, with a smaller energy consumption) is the considerable limitation in the functionality of the corresponding field device.
Depending on the particular application, the field devices must satisfy a most varied range of safety requirements. In order to satisfy the particular safety requirements (e.g. the SIL-standard “security integrity level”, which is important in process automation), the functionality of the field devices must be fashioned in a redundant and/or diverse manner.
Redundance means increased safety through doubled, or plural, design of all safety-relevant hardware and software components. Diversity means that the hardware components (e.g. microprocessors or A/D converters) located in the various measuring paths come from different manufacturers and/or are of different type. In the case of software-components, diversity requires that the software stored in the microprocessors originates from different sources, e.g. comes from different companies, or different programmers, as the case may be. Through all these measures, it should be assured that a safety-critical failure of the field device, as well as the occurrence of simultaneously arising systematic errors in the provision of measured values, are excluded with a high probability. It is also known additionally to design individual essential hardware and software components of the evaluating circuit in redundant and/or diverse manner. Through redundant and diverse design of individual hardware and software components, the degree of safety can further be increased.
An example of a safety-relevant application is fill-level monitoring in a tank in which a burnable or explosive liquid—or also a liquid which is not burnable, but instead presents a hazard to local waters—is stored. Here, it must be assured that the supply of liquid to the tank is immediately interrupted as soon as a maximum reliable fill level is reached. This, in turn, presupposes that the measuring device detects the fill level with a high reliability, and that the measuring device works faultlessly.
In WO 2009/062954 A1, a field device is described, which has a sensor functioning according to a defined measuring principle. Also present is a control/evaluation unit, which, as a function of a safety standard required for the particular safety-critical application, conditions and evaluates along at least two equal-valued measuring paths the measurement data delivered by the sensor. The control/evaluation unit is at least partially embodied as a reconfigurable logic chip having a plurality of partially dynamically reconfigurable function modules. In each case, the control/evaluation unit configures the function modules in the measuring paths as a function of the particular defined safety-critical application, and does so in such a manner, that the field device is designed according to the required safety standard.
Problematic in the case of the known embodiment is the fact that a malfunction (e.g. a short circuit or a temperature change) in one section automatically influences other sections. A crosstalk onto other sections takes place, meaning that the field device could deliver defective measurement results, and thus no longer works reliably. This presents a high risk in safety-critical applications, a situation which is not acceptable.